The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
An aircraft is propelled by several turbojet engines each housed in a nacelle.
A nacelle generally has a tubular structure comprising an air inlet upstream of the turbojet engine, a median section intended to surround a fan of the turbojet engine, a downstream section intended to surround the combustion chamber of the turbojet engine and to constitute the ejection nozzle of the flow of the fan of the engine that does not pass through the combustion chamber (secondary flow). This nozzle is commonly called secondary flow path or cold flow channel of the nacelle. This portion often includes a thrust reverser, a device for allowing obtaining aerodynamic braking of the aircraft during landing by returning the secondary flow forward.
This nacelle is intended to accommodate a bypass turbojet engine capable of generating via the blades of the rotating fan a hot air flow (also called primary flow), originating from the combustion chamber of the turbojet engine, and a cold air flow (secondary flow) already mentioned above. The outlet section of this nozzle is delimited by the outer trailing edge of the nacelle and the central body of this nacelle. This secondary ejection section controls the flow rate of air passing through the secondary nozzle and therefore governs to some extent the operation of the engine.
The optimum section of the ejection nozzle can be adapted according to the different phases of flight, namely the takeoff, climbing, cruise, descent and landing phases of the aircraft. It is indeed useful to be able to increase this section during the takeoff and landing phases, and to reduce it during cruise phases: this often relates to a nozzle with a variable outlet section, or else to “VFN” or “VAFN,” the acronym for “Variable Fan Nozzle” or “Variable Area Fan Nozzle.” The already well-known advantages of such variable-section nozzles, also called adaptive nozzles, consist in particular in noise reduction or fuel consumption decrease. In addition to that, it also allows ensuring the operation of the engine while avoiding engine pumping (too much compression rate with too little flow rate causes opening of the VAFN) or overspeed at the level of the fan rectifier (too much flow rate in the secondary flow path causes closure of the outlet section).
Among the various embodiments of ejection nozzles of the prior art, it is in particular known to perform the variation of the outlet section of the nozzle from pivoting panels positioned at a downstream end of the sliding thrust reverser cowl, rotatably mounted about an axis substantially transverse to a longitudinal axis of the nacelle. The pivoting of these panels causes a variation of the section of the secondary nozzle. This rotation is often coupled with a translation allowing to improve the aerodynamics of the device.
The panels of the nozzle, sometimes called “doors,” or even “flaps,” are typically associated with an actuation system piloted by the engine management system. In this case it is therefore important to be able to actuate the thrust reverser cowl and the panels of the adaptive nozzle independently. Particularly, the systems for maintaining the thrust reverser in folded flight position must in no case be impacted by the operation of the variable nozzle.
To perform this independent actuation, each movable part of the nacelle (thrust reverser cowl, nozzle panels) can be equipped with its own actuation system, and thus be driven independently. This relates to a segregated actuation of the nozzle panels and of the thrust reverser cowl.
An alternative to this segregated operating mode consists in mutualizing the actuation systems of the thrust reverser cowl and of the nozzle panels. For this purpose, a single system of actuators is used for the thrust reverser cowl and for the nozzle panels, and the thrust reverser is equipped with locking/unlocking means and with a system for coupling the actuators of the thrust reverser with the nozzle doors designed to authorize movement of the nozzle panels independently of the (locked) position of the thrust reverser sliding cowl. The actuators are then provided with a system allowing a displacement of the doors without moving the sliding cowl of the thrust reverser and, on the contrary, this system will not move the panels of the nozzle when the thrust reverser is deployed.
Regardless of the selected actuation system, whether segregated or mutualized, the actuation of the nozzle panels is performed by means of one or more actuator(s) substantially parallel to the longitudinal axis of the nacelle, these actuators controlling, via a movement transmission system (for example a suitable rod assembly), the rotation of one or more panel(s) of the nozzle. Thus, the forces generated at the actuators during the rotation of these nozzle panels are oriented along the longitudinal axis of the nacelle, and are transmitted in particular to the structure of the nacelle which approximates the movable panels of the nozzle. These longitudinal forces generated by the rotation of the nozzle panels appear to be very penalizing because they can cause axial scooping generating deformations of the structure of the nacelle which approximates the movable panels of the nozzle. The scooping effect is in addition further substantially increased when the thrust reverser cowl of the nacelle is an “O-duct” type cowl, that is to say a cowl in the form of a one-piece shroud.